This application claims the benefit of German Patent Application No. 100 38 006.9 filed on Aug. 4, 2000.
The invention relates to a laser amplifying system comprising a plate-like solid-state body which has two oppositely located flat sides and comprises a laser-active medium, a cooling member with a support surface which is arranged so as to face one of the flat sides of the solid-state body and with which this flat side is thermally coupled for the discharge of heat.
A laser amplifying system of this type is known, for example, from EP 0 632 551.
In the case of such a laser amplifying system, it has not been specified exactly how the solid-state body is intended to be connected to the cooling member.
In particular, it is essential for the connection between solid-state body and cooling member that the solid-state body which is, mechanically, very unstable on account of its slight thickness retains the desired shape and even when retaining its shape is subjected to as little mechanical stressing as possible during the operation of the laser amplifying system.
This object is accomplished in accordance with the invention, in a laser amplifying system of the type described at the outset, in that the flat side of the solid-state body is coupled mechanically and thermally to a support surface by an adhesive layer which is produced from an adhesive material which passes essentially invariant in volume from a liquid state into a solid, cross-linked state and that the adhesive layer has an active adhesive layer area with a heat resistance of less than 10 Kxc3x97mm2/W.
With this solution it is possible to fix the solid-state body, which is, mechanically, extremely sensitive, on the cooling member securely and without any appreciable mechanical deformations and, in this respect, to bring about a discharge of heat from the solid-state body which ensures an adequate cooling of the solid-state body via the cooling member without any restriction of the flow of heat from the solid-state body into the cooling member occurring as a result of the adhesive layer.
In this respect, the term xe2x80x9cessentially invariant in volumexe2x80x9d is to understood such that the adhesive displays a change in volume of less than 5%, even better less than 2% whilst passing from its liquid state into its solid, cross-linked state.
A particularly expedient embodiment of the inventive laser amplifying system provides for the heat resistance of the active adhesive layer area to be less than 5 Kxc3x97mm2/W, even better 2 Kxc3x97mm2/W.
With respect to the extension of the active adhesive layer area relative to the entire adhesive layer, no further details have so far been given. In principle, the active adhesive layer area could comprise the entire adhesive layer. The active adhesive layer area does, however, preferably comprise only a section of the adhesive layer.
In this respect, it is particularly favorable when the active adhesive layer area is at least that area of the adhesive layer which borders on a volume area of the solid-state body, in which a pumping power density of the pumping light radiation field of approximately 80% of the maximum value and more is present.
This means that the active adhesive layer area preferably serves to discharge the heat from the volume area of the solid-state body which is pumped to a considerable degree, namely the area of the solid-state body pumped with 80% of the pumping power density and more.
It is even more advantageous when the adhesive layer area is at least that area of the adhesive layer which borders on a volume area of the solid-state body, in which a pumping power density of the pumping light radiation field of approximately 70%, even between approximately 60% of the maximum value and more is present.
In addition, there is a further possibility of defining the active adhesive layer area in that the active adhesive layer area is at least that area of the adhesive layer which borders on the volume area of the solid-state body penetrated by the pumping light radiation field.
This definition covers, in particular, all the cases where the pumping light radiation field is coupled into the solid-state body via one of its flat sides.
A further, advantageous solution provides for the active adhesive layer area to be at least that area of the adhesive layer which borders on the volume area of the solid body penetrated by at least two intersecting pumping light radiation fields.
This definition of the volume area covers, on the one hand, all the cases where several pumping light radiation fields are coupled in through one flat side of the solid-state body but also the case where several pumping light radiation fields are coupled in via a narrow side of the solid-state body and intersect in a central area of the solid-state body, wherein the volume area is defined by the intersecting pumping light radiation fields.
In order to bring about, in addition, a sufficiently stable fixing of the solid-state body on the cooling member during operation of the laser amplifying system, it is preferably provided for the adhesive layer to have a tensile strength of more than 1 N/mm2.
In this respect, it is even better when the adhesive layer has a tensile strength of more than 5 N/mm2.
In addition, an adequately high shearing strength of the adhesive layer is also necessary within the scope of the invention solution. It is particularly favorable when the adhesive layer has a shearing strength of more than 5 N/mm2. It is even better when the adhesive layer has a shearing strength of more than 25 N/mm2.
Since, during operation of the laser amplifying system, the solid-state body is optically excited by a pumping light radiation field and thus also heated up thermally, a thermal heating up of the adhesive layer is also to be taken into account.
This thermal heating up of the adhesive layer leads in the case of many adhesives to a variation in shape brought about thermally.
Since the constant optical quality of the arrangement and shape of the solid-state body is of considerable importance for the inventive solution it is particularly advantageous within the scope of the inventive solution when the adhesive layer is essentially thermally invariant in shape in the solid, cross-linked state.
In this respect, the term xe2x80x9cessentially thermally invariant in shapexe2x80x9d is to be understood such that the adhesive layer displays at the most a maximum admissible change in shape of the solid-state body of 0.5 xcexcm, even better 0.1 xcexcm, in the temperature range of approximately 270 to approximately 360 Kelvin relevant for the inventive laser amplifying system.
With respect to the type of adhesive, no further details have so far been given. One advantageous embodiment, for example, provides for the adhesive to be a two-component adhesive since this is particularly suitable for fulfilling the requirements specified above.
An essentially volume-invariant behavior in accordance with the invention can, in particular, be achieved in a particularly simple manner when the adhesive passes from the liquid state into the solid, cross-linked state without any transfer of substances.
The term xe2x80x9cwithout any transfer of substancesxe2x80x9d is to be understood in this respect such that no exchange of substances whatsoever with the surroundings takes place, i.e. neither the absorption of substances, e.g. water vapor, nor the discharge of substances, e.g. solvents, or products of reaction, such as, for example, acetic acid, takes place during the hardening.
A particularly favorable variation provides for the adhesive to be an adhesive hardening by way of a supply of energy by means of radiation.
Such a supply of energy by means of radiation would, for example, also be the supply of energy by means of particle radiation or electromagnetic radiation.
In this respect it is particularly favorable when the adhesive is hardened by way of radiation with light.
A particularly preferred variation provides for the adhesive to be hardened by way of radiation with UV light.
Within the scope of the inventive solution described thus far, it has merely been explained in conjunction with the adhesive layer that this contains adhesive.
The viscosity of the adhesive in the non-cross-linked state has not so far been specified. In order to achieve particularly thin adhesive layers it is preferably provided for the adhesive to have a viscosity of less than 1000 mPaxc3x97s in the non-cross-linked state.
It is, however, also possible to alter the characteristics of the adhesive by adding filler materials to it.
In this respect, one particularly advantageous embodiment provides for the adhesive layer to be free from filler material since the use of an adhesive without any filler material allows, on the one hand, the viscosity of the adhesive to be kept as low as possible and, on the other hand, as a result the thickness of the adhesive layer can be kept particularly slight when no filler materials are present.
Another advantageous embodiment provides, however, for the adhesive layer to have a filler-material; such a filler material has the advantage that it creates the possibility of improving the heat resistance of the adhesive layer but, at least in some cases, at the expense of the minimum thickness of the adhesive layer which can be achieved and at the expense of the viscosity.
Another filler material could, for example, have nanoparticles which would offer the advantage that they allow a relatively thin adhesive layer.
Another solution provides for the filler material to have filler bodies with a size in the micrometer range.
With respect to the type of filler bodies it is advantageous when the filler material has filler bodies consisting of one or several of the substances boron nitride, diamond, silver, copper and/or gold.
With respect to the thickness of the adhesive layer, no further details have so far been given. Particularly in the case of an adhesive layer free from filler material it is advantageous when the adhesive layer area bordering on the active volume area has a thickness of less than 5 xcexcm. It is even better when the adhesive layer area bordering on the active volume area has a thickness of less than 2 xcexcm, even better of less than 1 xcexcm.
On the other hand, when using filler materials in the adhesive layer it is possible to configure this such that the adhesive layer area bordering on the active volume area has a thickness of less than 50 xcexcm, wherein the thickness of the adhesive layer area will, in this case as well, preferably be kept as thin as possible so that, for example, in the case of nanoparticles thicknesses of a few micrometers are likewise the aim.
With respect to the design of the optical properties of the adhesive layer, no further details have likewise been given thus far. In principle, the adhesive layer could be as required, for example, also non-transparent. It is, however, particularly favorable when the adhesive layer is optically transparent in order to bring about as slight a negative effect as possible on the optical properties of the solid-state body, in particular, any negative effect due to absorption of the adhesive.
With respect to the design of the adhesive layer itself, no further details have so far been given. One expedient embodiment, for example, provides for the adhesive layer to have an essentially constant thickness. In such a case, the effects on the optical quality of the solid-state body of changes in the volume of the adhesive layer at right angles to the support surface are slight since these occur essentially uniformly over the entire extension of the second flat side.
Another advantageous solution provides for the adhesive layer to have a thickness increasing in a radial direction starting from a center of the active volume area, proceeding from a central adhesive layer area bordering on this center. This solution has the advantage that the solid-state body can be placed on a drop of adhesive in a simple manner and this shape of the adhesive layer may be achieved by pressing on the solid-state body since, as a result, a displacement from the interior outwards and thus a relatively thin design of the adhesive layer may be achieved in a simple manner on account of the shape of the adhesive layer aimed for.
In this respect, it is particularly expedient when the course of the thickness of the adhesive layer is essentially radial symmetric to the center of the active volume area.